Big Four
From ACT Wiki
1.
In the professional services context, the Big 4 usually refers to the four largest international professional services firms and auditors.
2.
The term is also commonly used in banking, in different contexts.
For example, referring to the four largest banks in a given country or a given region.
The four largest UK banks in 2016, by total assets, were HSBC, Barclays, RBS and Lloyds.
